1. Field of the Invention
This invention relates to a rotational speed change amount detecting apparatus for an internal combustion engine, and more particularly to a rotational speed change amount detecting apparatus capable of detecting the amount of change in the rotational speed of an internal combustion engine such as a diesel engine with high accuracy.
2. Description of the Prior Art
In general, to conduct various controls in an internal combustion engine electronically, it is necessary to detect the rotational speed of the internal combustion engine with high accuracy. For example, in an electronically controlled governor, the gain of the control system is lowered and a filter in the form of a circuit having a small phase delay or a program providing an effect similar to such a filter is provided to attain stable operation of the engine. However, such a filter in the form of a circuit or program impairs the response characteristics of the control system when the engine load changes abruptly. It is therefore desired to detect changes in the load continuously and change the constant of the filter according to the detected result so as to provide a filter characteristic appropriate for the operation condition of the engine at each instant. For this reason, it has been proposed to detect the amount of change (.DELTA.N/.DELTA.T) in the engine speed N per unit time to determine the change in the load and to change the characteristic of the filter accordingly. However, it is necessary to detect the engine speed accurately to accomplish such control satisfactorily.
More specifically, in an internal combustion engine, induction, compression, power and exhaust strokes are effected in a predetermined cycle. Acceleration occurs only immediately after the power stroke so that the rotational speed of the engine varies periodically. For this reason, in order to be able to conduct controls on the basis of the rotational speed with high accuracy, it is required to obtain rotational speed data free from such periodic variation.